Sweetening process using ammonia as catalyst



United States Patent 3,250,697 SWEETENING PROCESS USING AMMONIA AS CATALYST Charles J. Walters, Ras Tanura, Robert E. Messinger, Dhahran, and John A. Schnautz, Ras Tanura, Saudi Arabia, assignors to Arabian American Oil Company, a corporation of New York No Drawing. Filed Dec. 12, 1963, Ser. No. 329,940 9 Claims. (Cl. 208-207) Our invention relates to a process for treating liquid crude petroleum hydrocarbons containing objectionable amounts of hydrogen sulfide and more specifically relates to a process for treating liquid petroleum crude oils to reduce the amount of hydrogen sulfide contained therein by converting it to an innocuous material.

In the handling of crude oils containing hydrogen sulfide, for example in storage in tanks or transportation on tankers or by other means, the hydrogen sulfide in the oil presents a danger to personnel due to the toxicity of hydrogen sulfide vapors over the crude oil. It is thus desirable to remove the hydrogen sulfide to obviate this problem.

Various methods have been employed to sweeten sour petroleum crudes by removing the hydrogen sulfide contained therein. A widely used method is based on thermal stripping techniques wherein a sour crude is charged to the top of a column containing bubble-cap trays. Passing down through the column the crude is stripped of hydrogen sulfide and light hydrocarbons by vapors driven oif the crude in a reboiler at the bottom of the column. The sweet crude is collected at the bottom of the column, cooled and pumped to tankage or to a pipeline. Obvious inherent disadvantages of such a method include a large capital investment for equipment and the necessity for a fully attended operation. The practice of our invention, however, is a substantial improve ment over such a method since it eliminates the need for bubble-cap trays and a fired or steam heated reboiler which in turn facilitates substantially unattended operation. Our invention also improves conservation of the charge by decreasing gravity loss from the crude oil.

Another currently practiced method of sweetening sour crudes consists of stripping the hydrogen sulfide from the crude oil with sweet gas. Generally, in this type of process sour crude flows down a column countercurrent to a stream of sweet gas which strips out the hydrogen sulfide. The practice of our invention is also a substantial improvement over this method since it eliminates the need for maintaining complex gas sweetening facilities with a savings in expenditures for equipment and labor. Moreover, no control is necessary to insure substantial non-removal from the crude oil of valuable hydrocarbon constituents by a sweetening gas.

Our invention provides an economically attractive process for sweetening a sour crude and reducing toxicity of vapors over the crude oil by decreasing at least a substantial proportion of the hydrogen sulfide content of the crude by conversion to an innocuous material.

We have found that by bringing together, in contact with crude liquid petroleum hydrocarbons containing objectionable quantities of hydrogen sulfide, an oxygencontaining gas and catalytic amounts of ammonia, the hydrogen sulfide content and thus the toxicity of vapors over the crude can be substantially decreased by conversion of the hydrogen sulfide to an innocuous material, elemental sulfur. We have further found that immediate processing of the treated liquid crude containing the elemental sulfur, formed in the liquid crude from the hydrogen sulfide, to remove the elemental sulfur is generally unnecessary in order to achieve a substantially non-corrosive fluid. Thus, liquid crude oil containing ice objectionable and potentially dangerous amounts of hydrogen sulfide can be effectively treated by our process to provide a crude safe for handling, particularly in transportation by tanker, without further processing.

In accordance with the process of the invention, an oxygen-containing gas and small catalytic amounts of ammonia are incorporated in a sour crude liquid petroleum. The order of introducing the reagents is not critical but it is preferred that intimate contacting of the gas and the liquid sour crude be established for a more efiicient sweetening operation. We have found that intimate contacting of the gas and liquid is important for high reaction rates. Preferably, therefore, the reaction is conducted in a packed column. The sweetening operation can be carried out in the absence of packing material but a less efficient operation results. However, the efficiency of an operation where no packing material is utilized can be materially increased when the time for the reaction can be conveniently lengthened. For example, one situation in which a more eflEicient operation can be realized, is in the pipeline transportation of the sour crude. Therefore, our invention also provides an economical method of pipeline sweetening of sour crude. Yet another representative situation can be a batch sweetening process in which the oxygen-containing gas and catalyst are brought into intimate contact with the confined sour crude petroleum.

The quantity of oxygen-containing gas present is that sufficient to oxidize the hydrogen sulfide completely to sulfur and it can be supplied to the reactor be it a packed column or to a pipeline or an open vessel, etc., by any convenient means. Generally, the quantity of oxygencontaining gas employed can be varied with good results. In general, a mole ratio of oxygen to hydrogen sulfide of from about 0.5 to about 7:1, preferably about 1.0 to 5:1, gives good results. When a packed column is used a mole ratio of about 24:1 is preferred. In pipeline sweetening, a mole ratio of about 12.5 :1 is preferred. It is preferred also to employ air as the source of oxygen in the process, but other oxygen-containing gases, can be used. When air is used it is supplied generally in amounts of about 2 to 30, preferably 4 to 20 times greater, by weight, than the hydrogen sulfide content of the crude petroleum. Preferably, in a packed column a continuous concurrent contact of the oxygen-containing gas and ammonia catalyst with the liquid crude is employed although the reaction can be carried out using countercurrent flow of the reactants or even in a batch type process by bubbling the gas into the crude being treated.

The amount of ammonia required is relatively small. The ammonia acts as a catalyst for the rapid oxidation of the hydrogen sulfide to sulfur. Oxidation of the hydrogen sulfide proceeds at a much lower rate without the presence of ammonia. It is believed that the overall reaction can be expressed by the following simplified equations:

We have found that more than the stoichiometric amount of ammonia for complete reaction with hydrogen sulfide, per Equation 1, usually does not increase the rate of oxidation and may in fact change the nature of the reaction if sufiicient ammonia is added to establish other than acidic conditions in the crude. We have found that as much as ninety-eight percent reduction in hydrogen sulfide content can be achievedwith less than 0.5 stoichiometric equivalents of ammonia. About 0.1 to 1 stoichiometric equivalents, preferably about 0.4 to 0.6 stoichiometric equivalents, of ammonia are sufficient to attain substantially complete conversion of the hydrogen sulfide in the crude oil. ammonia to hydrogen sulfide of about 0.2 to 2:1, preferably 0.8 to 1.2:1. Generally, the weight of ammonia present will be about 0.1 to 1.0 times the hydrogen sul- This corresponds to a molar ratio of 4 sweet crude for transportation by tanker or other means where sweet crude is desired because of the reduced toxicity of its vapors.

The following examples illustrate the process of the fide'content of the crude petroleum or about 2 to 13 5 invention in which crude petroleum oils having an API weight percent based on the air-ammonia crude sweetgravity range from about 28 to 38 were used. The oils ening agent. The ammonia can be introduced to the reused were Arabian crudes.

actor in a gaseous or liquid form. The ammonia is re EXAMPLE I generated and can be recovered for reuse if desired.

The process of our invfimion is operable with Fem} w A sour crude petroleum o1l havlng a hydrogen sulfide leum and petroleum products such as crude oil and the conten't 'f 500 P-P- was chargid. to the bOItQm distillate oils boiling within the range of from about 100 of a 3 X 3 Column at an p f fate of 25 P H1111- F. to about 750 F. The crude oil or distillate fraction The 001M011 w s p c ed-with a mass of inert gravel employed can contain up to about 500 hydrogen particles (9%" in diameter). Air was mtroduced at the sulfide or even more and the process of our invention 15 bottom h column a f" 25 Per efiectively reduces the amount of hydrogen sulfide to a ute"provldmg one stPlclllomemc equwalent of oxygen level safe for handling. By the process of our invention F air for Complete oxldatlm of the H25 to Sinful? F the :concentrattion of hydrogen sulfide of such oils can be mg to Equat10n5 I and above- Ammoma was reduced to a concentration of as low as 20 ppm. and defied togither Wlth tha a1r atan upflow of Per below. The process of our invention can be carried out l provlflmg one Stqwhwmetrwsqmvalenf of under a wide variety of conditions for bringing about conmOPIa Pccordmg to Equation I Q The column was tact between the liquid crude and the oxygen-containing mamtamado at a Pressure of 1 f a a tempera" gas to obtain sweetened crude. These conditions can inmm of 75 The Crude Petroleum liquid emuentfas volve combinations of various manipulative steps e.g. up- Well as a gas emuent from the column were analyzed 9 flow, downflow and horizontal flow of the liquid crude, g n sulfide content as well. The results of this concurrent and countercurrent flow of the gaseous sweet run are gwm m Table ening agent relative to the flow of liquid crude and the EXAMPLES II AND III use of solid contact materials, in the form of fixed, mov- Th e procedure of Example I was repeated agam except mg and fluidized beds. Preferably however the sweetening Process is carried out in a reactor wheriein the con- 3 g i zg gggggg ig igg i g l gg ifi gg f tact material effectively serves to disperse the two phases. Example The results are shawnpin Table I also The type of the packing used in a' specific instance will generally depend on particular existing conditions such EXAMPLE IV as the density, v scosity and veloc1ty of the liquid crude. The procgdure of EXamPlg I was repeatfid again Examples of suitable packing material lnclude stainless lowing the same'pmcedmes outlined except that only 2 steel wool, beads, pellets, lumps, chips find the like. of the ammonia equivalents according to Equation I were i s zi 5 4 g t crudelofl oftbfetween abolft employed. These results are also shown in Table I.

an mmu es 1s sa is ac cry. 11 cer am cases, res1 dence times as low as 10 and as high as 90 minutes can EXAMPLES V AND VI be 1156(1- 40 Following the same procedure and using one equivalent The temperature at which the process is carried out h f air and ammonia in Example V, a sour crude (1065 not pp to be crlmal Vaflable- Somewhat 1 petroleum was sweetened with the results shown in Table Vated temperatures p to about accelerate the I. In Example VI twice the ammonia equivalents were oxidation reaction and even higher temperatures can be used.

Table I on, Air NHa, 11 s in 11 s Equivalents Example 00.] cc] cc./ sweet crude (gas) min min. min. product, percent ppm. Air NH:

25 25 15 20 0.1 1 1 25 15 15 0.07 2 1 50 150 30 20 0.10 3 1 50 50 20 90 0.8 1 as 50 50 30 .110 1.0 1 1 50 50 so 100 1.0 1 2 1 Stoichiometric equivalents of oxygen as air and H 8 to S according to Equations I and II, above.

used. Elevated temperatures, however, are generally not preferred since they ordinarily require the use of a pressure above atmospheric in order to maintain the crude in liquid form. The time required for the completion of the oxidation reaction will be dependent somewhat upon the nature of the charge stock and upon the several variables of the process including the concentration of hydrogen sulfide, the temperature at which the treated composition is maintained, the quantity of oxygen-containing gas employed, the environment in which effective intimate contact takes place, i.e. in a packed column or in a pipeline or in an open Vessel, and the like. It is apparent that sufiicient time should be permitted to allow a reduction in the hydrogen sulfide concentration to the value desired which will usually be from a few minutes to sev ammonia required for oxidation 0 equivalent according to Equation I does not appreciably increase the reduction of the hydrogen sulfide concentration.

EXAMPLE VII Essentially the same procedures as outlined in Example I were followed again using the same amount of reactants eral hours. The process is particularly useful in providing as shown in Example IV. The liquid crude and gas efiiuent were alalyzed for their H 5 content with 90 p.p.m. H28 again being detected in the processed crude and 0.8% H 8 in the gas effluent. After the column was thus stabilized, the flow of ammonia to the column was discontinued with no change in the introduction of air and crude oil.

decrease in the H 8 content of a liquid sour crude can be advantageously achieved according to the process of the instant invention. The data also indicate that especially favorable results are achieved when the reactants are pre- 5 mixed before being introduced to the column and when The crude product was periodically analyzed after the the column is operated with concurrent flow of reactants. tllgszltgf ammonia was discontinued with the following EXAMPLES XIH XIV Sour crude petroleum having a hydrogen sulfide con- Time m 0 25 0 go 130 210 tents as indicated below in Table III was fed to the base of a reactor 12.5 feet in diameter and 51 feet high con- H 8 lncrude, p.p.m 9o 33 130 216 224 203 taining bubble-cap trays. Ammoniaand air were also introduced into the base of the column in the amounts also These results show the importance of the presence of mdwateebelow F fmi of m i and NH in the reaction. For instance it took only one hour 15 as are aga 1n the stolchlomemc eflulvalents before a rise in the H Value was observed qulred 1n the reactlon according to Equations I and II above. The gases and l1qu1ds passed concurrently up- EXAMPLE VH1 ward through the bubble-cap column and into an associ- A sour crude petroleum having a hydrogen sulfide conated separator vessel where off-gas was vented to the tent of about 350 p.p.m. was pro-mixed with air and 20 atmosphere. The sweetened crude oil was pumped to ammonia and fed to the bottom of a mild steel column tankage. The operating conditions of the column and the 20 feet in height and having a diameter of 1 foot and results of the tests are given below in Table HI.

Table III Pres- Resi- H S in crude Sour crude Temp. of sure of dence Air NHB Water, HIS Example feed rate column column time equivequivwt. removal,

(m.b.p.d.) F.) (p.s.i.a.) (min.) alents alents percent In Out percent p.p.m. p.p.m.

XIII 20 101 58 57. 6 11. 4 0. 55 0 224 56 75. 0 XIV- packed with stainless steel wool to a density of about 5 The results of these tests when compared to the relbs./ft. Sour crude oil was charged at the rate of sults obtained in the packed column tests indicate that 103 barrels per day (b.p.d.). Ammonia and oxygen as a more efiicient sweetening operation is achieved in a air were present in amounts of 1.0 and 10 stoichiometric packed column. The data again indicate that less than equi n re p y, according to the q n The 40 the stoichiometric equivalent of ammonia produces satisacked column was maintained at a pressure of 10 p.s.i.g. factory H 8 removal percentages, thus confirming the d a temperature of 110 F. The sweetened crude p proposition that ammonia acts as a catalyst in the liquid troleum liquid fil lent Was an yz for hydrogen Sulfide crude sweetening process. The tests also show that the content which was found to be 90 p.p.m. for a 74 percent presence f water i not essential to h process reducticlilni of the hydrogen sulfide concentration of the EXAMPLE r Sour c e EXAMPLES IXXII A sour crude petroleum having a hydrogen sulfide content of 262 p.p.m. was sweetened according to the The packed column of m l g g process and in a column as described in Examples a Sour crude petroleum.contalmng i fi 2 XIII-XIV. 1.1 equivalents of ammonia and 5 equivaabout 154% splfur Whlch Was pre'mlxedfwfi anllmoma lents of oxygen as air, according to the equations, were Crude was Introduced to.the bottom 0 t e co l a also introduced into the base of the column and the various Fates Shown l w m Ammolga was gases and liquid crude passed concurrently upward preslmt m.varymg stolchlomemc equlvalents' Xygen through the bubble-cap column into an associated sep- 35 was mtrodlmed at the the column arator vessel. The residence time in the column was thevconcurrept l flow rates also listed T e co 57.6 minutes. The column was maintained at a temumn was malntained at apress ure of 45 p.s.1.g. and atemdperature of and a mean pressure of 52 psia. Perature between 95 and 110 The Sweetened hqm A sample of the crude was analyzed and the H 8 content crude petroleum effluent was analyzed for hydrogen sulwas found to be 116 ppm for a 55] percent reduc fide C n The results are hsted belowtion. From the separator vessel and without venting off-gas to the atmosphere, the crude was pumped through Table II about 2500 feet of 14" pipe to tankage. The residence time in the pipe was 35.9 minutes. The crude leaving bou ,l Air NIgt His iszd the pipeline was analyzed and the H S content found was Example .pq equlvprimes 72 p.p.m. for an additional 38 percent reduction or an aunts alents crude overall 72 percent reduction of the H 5 in the feed initial- 240 10 0' 5 7O 1y charged to the column. i5 3 i3 32? 3% EXAMPLE XVI 820 barrels of a sour crude petroleum having a specific gravity of 372 API at 60 F. a hydrogen sulfide con- The amount of corrosion of the column was checked tent of 166 p.p.m. and maintained at a temperature of with a corrosometer and found to be less than 2 mils per 63 F. was introduced into a large open vessel to which year. A reduction of the gravity of the crudes was only 0.4 equivalents of ammonia were added and through about 02 API. These data also show that a substantial 75 which 2,500 standard cubic feet per hour of air were bubbled. The crude. was periodically analyzed for H S content with the following results:

Time

H 5 in crude p.p.m. Hrs. Min

When the crude was analyzed 52 p.p.m. H 8, i.e. a 68% reduction of the dissolved H 8, the flow of air was discontinued. After a 17 hour storage period the crude was again analyzed and the H 5 content had been further reduced to 19 p.p.m. for a 63 percent reduction of the H S content or an overall 81 percent reduction. The specific gravity of the sweetened crude was 36.5 API at 60 F.

Thus the foregoing examples show the elfectiveness of using small quantities of ammonia together with an oxygen containing gas to reduce the hydrogen sulfide content of a sour crude petroleum.

We claim:

1. A process of decreasing the hydrogen sulfide content of a sour liquid crude petroleum which comprises contacting said sour liquid crude petroleum with a catalyst consisting essentially of ammonia and with an oxygen-containing gas to oxidize'the hydrogen sulfide to a material which is innocuous during subsequent handling and transportation of the crude.

2. The process of claim 1 wherein the mole ratio of oxygen in the oxygen-containing gas to hydrogen sulfide is about 0.5-7:1 and the mole ratio of ammonia to hydrogen sulfide about 0.22: 1.

3. The process of decreasing the hydrogen sulfide content of a sour crude petroleum in the liquid phase which comprises passing the liquid crude and an oxygen-containing gas together with a catalyst consisting essentially of ammonia concurrently through a mass of solid packing material maintained within a contact zone to oxidize said hydrogen sulfide and recovering a liquid crude substantially reduced in hydrogen sulfide content.

4. The process of claim 3 wherein the mole ratio of oxygen in the oxygen-containing gas to hydrogen sulfide 8 is about 0.5-7z1 and the mole ratio of ammonia to hydrogen sulfide about 0.2-2z1.

5. The process of claim 3 wherein the mole ratio of oxygen in the oxygen-containing gas to hydrogen sulfide is about 24:31 and the mole ratio of ammonia to hydrogren sulfide is about 0.8-1.2:1.

6. The process of decerasing the hydrogen sulfide content of a sour liquid crude petroleum confined in a pipeline which comprises contacting said confined liquid crude with an oxygen-containing gas, the mole ratio of oxygen in said oxygen-containing gas to said hydrogen sulfide being about 0.5-7z1, and with a catalyst consisting essentially of ammonia, the mole ratio of ammonia to hydrogen sulfide being about 0.22:l, to oxidize said hydrogen sulfide and recovering a liquid crude substantially reduced in hydrogen sulfide content.

7. The process of claim 6 wherein the mole ratio of oxygen in the oxygen-containing gas to hydrogen sulfide is about 12.5 :1 and the mole ratio of ammonia to hydrogen sulfide is about 0.8-1.2: 1.

8. The process for sweetening sour liquid crude pepetroleum containing hydrogen sulfide which cornprises reacting said sour liquid crude petroleum with an oxidizing gas in contact with a catalyst consisting essentially of ammonia.

9. The process of claim 8 wherein the oxidizing agent is air supplied in amounts of about 2 to 30 times greater by weight than the hydrogen sulfide content of said crude petroleum and the ammonia catalyst is supplied in amounts of about 0.1 to 1.0 times the Weight of the hydrogen sulfide present.

References Cited by the Examiner UNITED STATES PATENTS 1,423,712 7/ 1922 Clancy 208-236 1,971,172 8/ 1934 Benedict 208-236 2,253,011 8/1941 Benedict 208-208 X 2,828,247 3/1958 Bowers 208-207 X 2,853,43 1 9/ 1958 Bowers 208207 FOREIGN PATENTS 596,358 4/ 1960 Canada.

DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

R. H. SHUBERT, Assistant Examiner. 

1. A PROCESS OF DECREASING THE HYDROGEN SULFIDE CONTENT OF A SOUR LIQUID CRUDE PETROLEUM WHICH COMPRISES CONTACTING SAID SOUR LIQUID CRUDE PETROLEUM WITH A CATALYST CONSISTING ESSENTIALLY OF AMMONIA AND WITH AN OXYGEN-CONTAINING GAS TO OXIDIZE THE HYDROGEN SULFIDE TO A MATERIAL WHICH IS INNOCUOUS DURING SUBSEQUENT HANDLING AND TRANSPORTATION OF THE CRUDE. 